Detection of impulse control behaviours in Parkinson's disease: incremental yield of unstructured psychiatric interviews over QUIP screening and routine clinical assessment

Background. Impulse control behaviours (ICBs) are common but frequently under-recognised non-motor complications of Parkinson's disease (PD), arising from dopaminergic overstimulation of fronto-striatal reward circuits. Standardised self-report tools such as the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease (QUIP) are limited by reduced insight, recall bias and reluctance to disclose sensitive behaviours. Objectives. To compare three sequential approaches to ICB detection in PD - routine outpatient referral documentation, QUIP screening, and a clinician-led unstructured psychiatric interview (UPI) integrating informant testimony - and to characterise the spectrum and co-occurrence of ICB subtypes. Methods. In this prospective observational single-centre study, 144 consecutive inpatients with idiopathic PD were systematically evaluated at admission to a specialised neuropsychiatric unit by the three sequential approaches above. Detection rates were compared using McNemar's test. Results. ICBs were identified in 13.2% via referral data, 20.8% via QUIP and 36.1% via UPI (pairwise McNemar p < 0.001). UPI yielded a 15.3-percentage-point increment over QUIP, including detection of reckless generosity (not represented in QUIP item content) and clinically relevant presentations of dopamine dysregulation syndrome and punding that were under-detected by brief screening items. Multiple co-occurring ICBs were common: 27.8% of patients exhibited two or more subtypes, 14.6% four or more, and 2.1% up to seven. Patients with ≥ 6 ICBs were uniformly male, dopamine agonist-treated, younger and had longer disease duration. Conclusions. Routine clinical assessment and self-report screening substantially underestimate the prevalence and complexity of ICBs in PD. A brief informant-supported psychiatric interview improves detection and reveals clinically relevant phenotypic clustering, with implications for dopaminergic therapy adjustment and pre-DBS evaluation.